Page margin at-rule CSSOM support.
Add the CSSMarginRule interface, which is available via the CSSRuleList
cssRules member inside a CSSPageRule.
Parsing of CSS margin rules is protected by the feature flag
PageMarginBoxes, so unless that feature is enabled, the list of margin
rules will always be empty.
Bug: 324827379
Change-Id: I76da73a4b98a276ee59533993f52511bca72a42f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5301160
Commit-Queue: Morten Stenshorne mstensho@chromium.org
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1320945}